The demand for increased speeds and reduced costs in communication systems keeps growing, due in large part to the increase in mobile device usage, streaming media services, cloud computing, and big data analysis. Semiconductor waveguide, e.g. silicon, photonics has become the most promising technology to provide high-speed, low energy consumption and low cost next-generation data communication systems.
Active devices, including photodetectors (PD), are a critical part of photonics integrated circuits (PIC), particularly for semiconductor waveguide, e.g. silicon, photonics (SiPh). A photodetector with high responsivity will compensate the channel insertion loss, and help fulfill the required link power budget. Several semiconductor absorbing materials, e.g. indium gallium arsenide (InGaAs), gallium phosphide (GaP), Silicon (Si) and Germanium (Ge), may be used, but Germanium, which may be epitaxially grown on Silicon, is the preferred absorber material, due to its compatibility with complementary metal oxide semiconductor (CMOS) fabrication processes. An example of a semiconductor photodiode is disclosed in U.S. Pat. No. 9,553,222, issued Jan. 24, 2017, which is incorporated herein by reference.
However due to sensitivity of PICs to back reflection, it is important to design photodiode elements with low back reflection. Currently back reflection of slightly lower than −30 dB has been demonstrated. Back reflection of individual PIC components becomes a large bottleneck for scaling PIC devices for higher performance applications. It is important to lower back reflection of individual component, particularly for active elements, without compromising the device performance. In a conventional photodetector 1, illustrated in FIGS. 1 and 2, a semiconductor waveguide, e.g. silicon, 2 is mounted on a substrate 3 by any conventional manner, e.g. SOI, with a slab of light absorbing material 4, e.g. germanium, deposited thereon. For the PD device 1 the introduction of the absorbing material 4, causes the effective index of the optical mode 5 to experience abrupt change that may result in part of the light reflecting back.
An object of the present invention is to overcome the shortcomings of the prior art by providing a semiconductor photodetector with reduced back reflection.